Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the engine to the transmission or for the transfer of power in a transfer case. In continuously variable transmissions, power transmission chains or chain-belts are used to transfer power between a pair of variable pulleys. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. Each link has a body with a pair of spaced apertures and the apertures of one set of links are arranged and aligned with the apertures of the next adjacent set of interleaved links. Guide links are typically provided on the outside of the rows of links. The guide links are not designed to provide a driving contact, or power transfer, between the chain and the sprocket tooth. The guide links are intended to maintain the chain on the sprocket.
The inside or inverted tooth links have a pair of depending toes separated by a crotch. The links are connected by pivot means, which are typically round pins received in the apertures. The pivot means can also be rocker joints, which consist of pins and rockers. In a rocker joint chain, the pins rock against an associated rocker or aperture side. While the inverted tooth links pivot with respect to the pins, the ends of the pins are generally press fit into the apertures of the guide links to prevent rotation therewith. The pins are secured into the guide links by any means known in the art, such as caulking or welding, and are typically peened over on their ends. An example of a silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference. An example of a silent chain which can be used in engine timing applications is found in U.S. Pat. No. 4,759,740, which is also incorporated herein by reference.
Another type of chain is known as a "roller chain". A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, consist of spaced link plates, or sidebars, with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links, which are also known as "guide" links, consist of spaced link plates, or sidebars, with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. The rollerless chain contains bushings that directly contact the sprocket. Both types of roller chains are typically specified in industry as British standard chain and American National Standards Institute (ANSI) chain.
Another type of power transmission chain is used to transfer power between a pair of variable pulleys in a continuously variable transmission (CVT). The chain links are provided in sets that are interleaved together and have aligned apertures in the links that receive pivot means. Load blocks are positioned on the chain between the spaced pivot members and provide the means for transfer of power between the pulleys. The load blocks can be in the form of struts that are carried in a passageway below the links. Alternatively, the load blocks can extend around the links of the chain and have one or more windows for receiving the chain. The load blocks have tapered outer or end surfaces which engage the sheave faces of the pulleys to provide the driving engagement between the pulleys and the chain.
The pivot joints of a CVT typically include a pin and associated rocker to provide articulation of the links. The pins are generally press fit into the outside row of links. In certain types of CVT chains, the outside row of links comprises guide links which are provided for securing the pins. An example of power transmission chain suitable for use in a variable pulley transmission is shown in U.S. Pat. No. 4,911,682, and U.S. Pat. No. 4,507,106, which are incorporated herein by reference.
A conventional power transmission drive is comprised of either a silent chain or a roller chain wrapped about at least two sprockets supported by shafts, or a CVT chain wrapped about a pair of variable pulleys. The chain is endless and assembled from interconnected links that are adaptable to fit over and about teeth formed on the sprockets. Movement of a driving sprocket causes power transmission through the chain and consequent movement of at least one driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. Timing drive applications can also include the use of a power transmission chain in the camshaft to camshaft drive in an overhead camshaft engine.
As described above, the pivot joints of a conventional silent chain, roller chain or CVT chain-belt typically include either round pins or rocker joints. In the round pin design, a generally round pin is fitted in a corresponding round aperture in the inverted tooth links or inside roller links. The round pin slides in the aperture as the links articulate around the sprocket. The round pins are press fit and secured into a guide link aperture on the outside of the chain. Similarly, the pins of a rocker joint are generally of greater length than the associated rocker and the pins are therefore press fit and secured into the aperture of the guide link on the outside row.
The present invention is an attempt to address the problem of unequal load sharing on the links across the length of the pins. Because the pins are normally press fit into the outer guide link apertures, the stiffness of the outer links tends to be greater than that of the inner links, which leads to unequal load sharing and pin bending. In the past, the uneven loads acting on the inner and outer links have been balanced by strengthening the inner links rather than weakening the outer links. The inner links have typically been strengthened by using a higher strength material, increasing their thickness, or doubling the links together to form a double-thickness link. The inner links have also been strengthened relative to the outer links by varying their lacing configuration to allow a desired amount of additional material to be added to end regions of the links. In U.S. Pat. No. 5,147,251, the disclosure of which is incorporated herein by reference, a three-way lacing configuration of a CVT belt is disclosed in which inner links in adjacent rows are staggered transversely in a lacing pattern which repeats every third row. To balance the tensile forces across the width of the chain, the links have varying thicknesses. In addition, the connecting elements have irregularly shaped end portions which are match-fit into similarly shaped apertures in the guide links.
Attempts have also been made at modifying the contour or configuration of the guide links to balance the forces acting on the guide links and toothed links. For example, U.S. Pat. No. 2,602,344 discloses a silent chain guide link having a crotch extending from the peripheral edge of the lower portion thereof and disposed between the pin apertures. The crotch compensates for the deflection or extension of toothed links to provide a balanced chain construction and distribute the shear loads across the chain pins evenly. The chain pins are the traditional rocker type pins which are fixedly secured to each aperture such that convex surfaces of adjacent pins bear against each other and allow pivotal movement of one link relative to another.
U.S. Pat. No. 4,227,425 discloses a self-centering joint comprising round apertures formed in the ends of both inner and outer link members. The apertures are larger in diameter than the cylindrical pins extending therethrough to provide clearance for the rocking joint action of the links on the pins. The pins have a ring portion for retaining the outer links and are free to rotate independently of the inner and outer links.
The present invention addresses the problem of unequal load sharing by providing a press fit of the pins into upper and lower edge portions of the outer guide link apertures while providing a space between the pins and the side edges of the apertures to balance the load acting upon the inner and outer links.